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The Darwinian progressive subsidence model for the evolution of fringing reefs, barrier reefs and atolls has been generally
accepted following the indisputable proof of subsidence provided by drilling results in the Pacific. Nonetheless, there are
data that do not fit the expectations of the model, such as the similar lagoon depths of barrier reefs and atolls as opposed
to the subsidence theory’s implicit prediction that atolls should have significantly greater depths. In contrast, a great
deal of evidence supports the influence of meteoric solution on barrier reef morphology. For example, the maximum lagoon depth
of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall. These modern
rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall, even
though the absolute amounts of such rainfall are unknown. The correlation therefore suggests the importance of Pleistocene
subaerial solution in contributing to barrier reef morphology. Further support for antecedent influence occurs in the form
of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes. On a larger scale,
the Cook Island of Mangaia provides evidence that solution can produce barrier reef morphology independent of reef development.
In contrast, there are no examples of the subsidence-predicted lagoon transition of fringing reefs to barrier reefs to atolls.
Moreover, the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their ‘presumed
progressive evolutionary development. Consequently, the evidence to date suggests that a solution morphology template has
been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today. The importance of subsidence
would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing
to lagoon depth variation among the larger continental entities.
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Donna Marie Bilkovic 《Estuaries and Coasts》2011,34(1):129-147
To investigate the effects of dredging and associated development pressures (i.e., shoreline armoring, developed land use)
on fish, three sets of paired dredged and undredged tidal creeks were surveyed within Lynnhaven River, Virginia. Fish species
diversity, community abundance, biomass, and size structure were compared among creeks and related to watershed, shoreline,
and physicochemical characteristics. Mean fish community characteristics (e.g., abundance) were similar among creeks; however,
species-specific analysis revealed subtle differences. Species biomass differed between dredged and undredged creeks, though
species abundance was similar. Turbidity highly influenced differences in species abundance among creeks, while organic matter,
dissolved oxygen, turbidity, and shoreline hardening may be influencing biomass patterns. The most recently dredged creek
appeared to provide less suitable nursery habitat for some species than historically dredged creeks, suggesting initial adverse
effects with eventual recovery. Protective measures, such as preservation of marshes, dredge depth, and time-of-year restrictions,
may be moderating development and dredging pressures. 相似文献
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南沙群岛珊瑚礁区仙掌藻的现代沉积特征 总被引：4，自引：0，他引：4
仙掌藻为温暖水体中钙化的绿藻,是南沙群岛珊瑚礁区重要的钙质沉积物源。对南沙群岛８座环礁现代沉积物样品的分析表明,仙掌藻碎屑在环礁各地貌沉积带沉积物中的含量,以泻湖盆底最高,平均为32.66％,最高可达75％,泻湖坡次之,平均9.22％,礁坪含量低,平均6.06％。南沙群岛仙掌藻以砂质基底上生长的直立类型为主,能生长于各个地貌沉积带,最适生态环境为封闭性好、泻湖面积大、水深较大（10～25m）、水动力弱的砂质泻湖盆底。仙掌藻的现代沉积特征反映了其生态特征,可作为中新世以来珊瑚礁沉积相划分的依据。 相似文献
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Carbonate sediment transport pathways based on foraminifera: case study from Frank Sound, Grand Cayman, British West Indies 总被引：2，自引：0，他引：2
Foraminifera can be used to determine the source(s) of carbonate sediment and the directions of sediment transport in shallow, coastal lagoons such as Frank Sound on the south-central coast of Grand Cayman. These determinations, based on the distribution of foraminiferal assemblages and ‘tracer species’ (numerically abundant species that live in known physiographic units and/or ecological conditions), show that the lagoonal sediments are a mixture of grains that originated in the lagoon and forereef. The variable proportions of these foraminifera throughout the lagoon reflects the dynamic processes that control lagoonal sedimentation. Amphistegina gibbosa, Discorbis rosea, and Asterigerina carinata lived in the forereef environment. The fact that these ‘tracer species’ are found throughout Frank Sound and in the beach sands, shows that they were transported across the reef crest and the lagoon. Abrasion-resistant Archaias angulatus, a‘tracer species’ indicative of a lagoonal setting, forms up to 50% of foraminiferal assemblages found in the lagoonal sediments. Preferential winnowing of small tests from these populations indicates sorting under high energy conditions. The vertical distribution of the forereef and lagoonal foraminifera in the sediment blanket that covers the floor of Frank Sound indicates that these processes are temporally persistent. Transportation of forereef foraminifera into and around the lagoon and sorting of the lagoonal foraminifera cannot take place under ‘normal’ conditions when the tranquil lagoon is characterized by weak currents. Storms and/or hurricanes, however, generate short-lived high-energy events that can move and sort the sediment and foraminifera. At the height of a storm, water and sediment are moved over the reef and then piled and held onshore by the onshore winds and the constant flow of water over the reef and across the lagoon. These currents can mix some of the lagoonal and forereef sediments. As a storm wanes, however, the ‘piled water’ flows offshore via strong rip currents that pass into the ocean through the channels which transect the reef. These currents winnow and/or strip sediment from the lagoon and may transport lagoonal sediments into the forereef area. As a result, residual lagoonal sediment is commonly characterized by larger and abrasion-resistant foraminifera. 相似文献
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《Australian Journal of Earth Sciences》2013,60(6):847-857
Elizabeth and Middleton Reefs are atoll-like structures that have developed on top of volcanic edifices and are close to the southern environmental limit of reef development in the southwest Pacific. Reef morphology and vertical accretion rates during the Holocene appear similar to those on other more tropical reefs. Sediment samples were collected from the lagoon of both reefs and around the flanks of Middleton Reef. A distinctly chlorozoan assemblage was observed with coral, molluscs, Halimeda, coralline algae and foraminifers being the dominant sediment constituents. Lagoon sediment samples show little variation within or between reefs, lacking the concentric zonation characteristic of larger atolls. Samples collected from the flanks of Middleton Reef, and subsurface material from vibrocores, differ compositionally from the surficial lagoon sand and were typically more tropical in character. A comparison of the sediment constituents from these reefs with those of samples from within a fringing reef and from the shelf around Lord Howe Island, further south, indicated regional patterns in sediment composition. Halimeda rapidly decreased in abundance with increased latitude, and appeared confined to deeper water, whereas coralline red algae increased significantly. The rapid change in these major sediment contributors is coincident with the general decrease in coral growth rates with latitude. This reinforces the notion that the latitudinal limit of reef development is constrained by factors other than coral growth alone. 相似文献
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脊槽地貌（Spur and Groove）是现代珊瑚礁礁坪和礁前的典型地貌,其发育特征是揭示珊瑚礁形成与演化过程的重要基础,目前有关环礁各地貌带脊槽地貌形态及成因的研究仍较为薄弱。南海南沙群岛岛礁脊槽地貌发育,是进行相关研究的理想区域。本文以南沙群岛北部道明群礁东北库归沙洲的典型脊槽地貌为研究对象,基于多波束测深数据,借助小波分析和过零点分析等方法,对环礁脊槽地貌形态参数进行定量研究。结果表明：库归沙洲各地貌带脊槽发育平均起始水深为15~16 m,主要为深水脊槽,最大起始水深相差较大（达8 m）,而终止水深相似（平均为16 m左右）。脊槽高差在礁前斜坡和内礁坪为2.15 m左右,在潟湖坡为1.24 m;平均槽宽在礁前斜坡为47.30 m,在潟湖坡达54.92 m。因此,在礁前斜坡脊槽发育相对密集且高差大,潟湖坡脊槽发育相对稀疏且高差小。从礁前斜坡至潟湖坡,脊槽边坡坡度逐渐增大,由“V”型脊槽向“U”型脊槽过渡,槽谷由左倾逐渐转化为右倾。同时,在内礁坪和潟湖坡多发育次一级脊槽,“V”型和“U”型共存。与全球代表性珊瑚礁脊槽形态的对比分析表明：南海地区各环礁多发育深水脊槽,其槽宽和延伸长度的关系部分符合波浪侵蚀作用主控的“V”型脊槽的拟合直线,部分符合生物建造作用主控的“U”型脊槽的拟合直线,表明其可能受上述两个作用共同控制,不同地貌带两者相对强弱不同。同时,频繁的热带风暴的破坏作用可能也是一个要因。 相似文献
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西藏羌塘盆地中侏罗世布曲期及夏里期岩相古地理与油气远景 总被引：4，自引：1，他引：3
在露头剖面地层学及沉积学研究的基础上,采用单因素分析多因素综合作图法,编制了西藏羌塘盆地中侏罗世布曲期和夏里期的单因素图和岩相古地理图。布曲期以碳酸盐岩沉积为主,自北而南依次发育局限台地（潮坪、泻湖）、开阔台地（台盆、浅滩/点礁）、台缘礁/浅滩、台缘斜坡、盆地等沉积（亚）相;夏里期以陆源碎屑沉积为主,发育泻湖、潮坪、滨岸、陆棚等沉积（亚）相。布曲组台盆和泻湖相泥灰岩和泥晶灰岩是良好的烃源岩,台缘礁和浅滩相碳酸盐岩是良好的储集岩,而上覆的夏里组泻湖和潮坪相泥岩和膏盐层是良好的区域性盖层,共同构成良好的生、储、盖组合。该生储盖组合大都被上覆的上侏罗统、白垩系、第三系覆盖。因此,布曲组是盆地内最好的油气勘探目的层,沿中央隆起带两侧以及北羌塘地区的琵琶湖－半岛湖凸起一带应是油气勘探的有利区带。 相似文献
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EUGENE C. RANKEY 《Sedimentology》2011,58(7):1831-1859
Islands rimming Pacific atolls typically form narrow, low‐lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea‐level rise. As these, low islands form the only habitable land for many island nations, understanding the character of shorelines, and the rates and controls that operate to bring about changes, is an issue of central importance. The purpose of this study is to unravel the characteristics of coastal change on atoll islands of the Gilbert Island chain of the equatorial Pacific nation of Kiribati, especially as they relate to autogenic shoreline processes and El Niño/Southern Oscillation variability. Integration of field observations, differential global positioning system data, historical aerial photographs and ultra‐high resolution remote sensing images demonstrates the nature, spatial patterns and rates of change from 17 islands on Maiana and Aranuka atolls. The results illustrate that, between 2005 and 2009, ca 50% of the shorelines on these islands displayed a discernable shift in position; some shorelines were accretionary (at net rates up to ca 8 m year?1) and others were erosional (up to ca 18 m year?1). Long‐term net rates of change on Maiana between 1969 and 2009 were lower than short‐term net rates measured between 2005 and 2009. Both short‐term and long‐term observations illustrate some of the greatest change occur near terminations of the largest, north–south oriented islands, associated with longshore movement of coarse sand and gravel. Direct hits by tropical depressions and marked seasonality, factors interpreted as being essential in island growth and shoreline dynamics elsewhere, do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics. Similarly, observations over four years suggested that shoreline variability probably is not influenced directly by marked sea‐level change, although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long‐term increase in the rate of sea‐level rise. Within this framework of global change, local anthropogenic effects, autogenic shoreline processes and El Niño/Southern Oscillation‐influenced wind and wave variability control many aspects of these dynamic shorelines. These results provide quantitative insights into the character and variability of rates of shoreline change, information essential for evaluating and mitigating the vulnerability of island nations such as Kiribati. 相似文献
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Kaneohe Bay, Hawaii, is an estuary used as a harbor for a military installation and for recreation, fishing, and research
purposes. Rapid shoaling of the bay had been reported and attributed to increased stream erosion and sedimentation from the
newly suburbanized watershed. Comparison of a 1976 bathymetric survey of Kaneohe Bay with that of a 1927 survey indicates
an average shoaling of the lagoonal area of 1.0 m. Average shoaling for the north and middle bay at 0.6m/49 years (1.2 cm
yr−1 is lower than for the south bay at 1.5m/49 years (3.1 cm yr−1). The total lagoonal fill in the 49-year period is about 1.95× 107 m3, assigned as follows: 64% carbonate detritus from the reefs as well as growth of living coral and unrecorded dredging spill,
9% recorded dredging spoils, and only 27% terrigenous sediment. Seismic reflection profiles distinguish spoil from natural
sediment and show that the infilling sediment is trapped between, burying reef structures built during Quaternary lower stands
of the sea. There had been little obvious change between 1882 and 1927 surveys. All information suggests that increased shoaling
rates since 1927 are due to reported and unreported disposal of dredge spoil, mainly from 1939 to 1945 for ship and seaplane
channels in the south bay, and not from increased runoff and urbanization around the south bay.
Hawaii Institute of Geophysics Contribution No. 1257. 相似文献
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Michael J. O'Leary Christopher T. Perry Simon J. Beavington-Penney John R. Turner 《Sedimentary Geology》2009,219(1-4):169-179
Assessments of carbonate platform reef–lagoon sediments and benthic habitats around Rodrigues Island (south-west Indian Ocean) have been undertaken in order to examine carbonate sediment textural properties and the controls on texturally-defined sediment fabrics. Reef–lagoon sediments, sampled from across the expansive (~ 8 km wide) carbonate-dominated windward platform, principally comprise poorly sorted medium- to coarse-grained bioclastic sands, composed of a low diversity of grain constituents — predominantly non-geniculate coralline algal bioclasts. Despite a marked homogeneity in sediment compositional and grain size properties, eight distinct sediment textural groups can be identified that form a heterogeneous mosaic across the contemporary reef–lagoon system. Only along the narrow outer platform margins (reef crest, sand apron and outermost lagoon environments) do we observe consistent (predictable) transitions in sediment textural groups, where physical processes are the primary drivers of selective sediment transport and sorting. In contrast, across the main expanse of the lagoon, the sediment substrates are characterised by an irregular mosaic of texturally-defined sediment groups — formed primarily as a function of sediment bio-retexturing. The burrowing activities of alpheid and callianassid shrimps are particularly important in this respect and impart a distinctly unique textural fabric to the upper sediment horizons in the environments in which the respective organisms occur. The consequence of this is that, at the platform system scale, individual, texturally-defined sediment groups are relatively poor indicators of prevailing hydrodynamic regimes or of local sediment production, reflecting more the biological action of organisms inhabiting the substrate. This has important implications for understanding the development of carbonate sediment fabrics in the context of palaeoenvironmental reconstructions and for interpreting a key diagnostic criteria of carbonate microfacies. 相似文献
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Beach erosion under rising sea‐level modulated by coastal geomorphology and sediment availability on carbonate reef‐fringed island coasts 
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下载免费PDF全文 Bradley M. Romine Charles H. Fletcher L. Neil Frazer Tiffany R. Anderson 《Sedimentology》2016,63(5):1321-1332
This study addresses gaps in understanding the relative roles of sea‐level change, coastal geomorphology and sediment availability in driving beach erosion at the scale of individual beaches. Patterns of historical shoreline change are examined for spatial relationships to geomorphology and for temporal relationships to late‐Holocene and modern sea‐level change. The study area shoreline on the north‐east coast of Oahu, Hawaii, is characterized by a series of kilometre‐long beaches with repeated headland‐embayed morphology fronted by a carbonate fringing reef. The beaches are the seaward edge of a carbonate sand‐rich coastal strand plain, a common morphological setting in tectonically stable tropical island coasts. Multiple lines of geological evidence indicate that the strand plain prograded atop a fringing reef platform during a period of late‐Holocene sea‐level fall. Analysis of historical shoreline changes indicates an overall trend of erosion (shoreline recession) along headland sections of beach and an overall trend of stable to accreting beaches along adjoining embayed sections. Eighty‐eight per cent of headland beaches eroded over the past century at an average rate of ?0·12 ± 0·03 m yr?1. In contrast, 56% of embayed beaches accreted at an average rate of 0·04 ± 0·03 m yr?1. Given over a century of global (and local) sea‐level rise, the data indicate that embayed beaches are showing remarkable resiliency. The pattern of headland beach erosion and stable to accreting embayments suggests a shift from accretion to erosion particular to the headland beaches with the initiation of modern sea‐level rise. These results emphasize the need to account for localized variations in beach erosion related to geomorphology and alongshore sediment transport in attempting to forecast future shoreline change under increasing sea‐level rise. 相似文献
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The concurrent development of a cool-carbonate Miocene clinoform system and the tropical reef which developed on its shelf in the North Carnarvon Basin is studied. The study, based on seismic interpretation and geometrical analysis, seeks to investigate how the architecture of the clinoforms develops in relation to the advance of the reef-margin, providing a proxy for discussing contemporaneous shoreline versus shelf-edge development. The progradation of the reef and shelf-edge often display a closely mirrored development, although the reef twice advances an order of two to three times the concurrent advance of the shelf-edge. The forced regression of the second advance, as compared to the normal regression during the first, is observed in proportionally higher input of sediment towards advance of the shelf-edge and toe, along with a gentler slope. The inability of the shelf-edge to keep pace with the reef-margin (and by proxy the shoreline) during lower accommodation/sedimentation is a result of the increased volume of sediment required to match reef-margin advance beyond the shelf-edge. Increased accommodation/sedimentation ratios promote higher trajectories where the volumes on shelf and slope are more balanced and the development more closely matched. The observed matched development of reef and shelf-edge during both limited and increased slope sedimentation, suggest that accommodation is the dominant control on the location and trajectory of both ‘shoreline’ and shelf-edge, and that excess sediment is deposited along the slope. 相似文献
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Two surface‐sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back‐reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain‐size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef‐flat to the back‐reef, but this transport is episodic and occurs principally during high‐tide stages. Sediment transport trends revealed by the grain‐size trend analysis method show onshore and alongshore low‐energy transport processes that are in agreement with the hydrodynamic records. The grain‐size trend analysis method also provides evidence of an offshore high‐energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain‐size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back‐reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones. 相似文献
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Linking pattern to process in reef sediment dynamics at Lady Musgrave Island,southern Great Barrier Reef 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 Sarah M. Hamylton Rafael C. Carvalho Stephanie Duce Chris M. Roelfsema Ana Vila‐Concejo 《Sedimentology》2016,63(6):1634-1650
Linking surficial sediment patterns in reef environments to the processes that underlie their depositional dynamics enables predictions to be made of how environmental changes will influence reef‐associated sedimentary landforms, such as islands and beaches. Geomorphic linkages between sediment deposition patterns and the biophysical processes that drive them are often poorly resolved, particularly at broad landscape scales where tangible statements can be made about structural changes to landforms. The present study applies geospatial techniques to link patterns in reef sediment dynamics at Lady Musgrave Island to the underlying processes driving them. In situ calcification is characterized by developing a high resolution map of the surficial calcium carbonate producing communities inhabiting the reef platform, and associated sediments across the reef flat are analysed for grain size, kurtosis, sorting and threshold bed shear stress to explore transport pathways across the reef flat and lagoon. Wave energy is modelled across the entire reef platform as a potential driver of sediment dynamics, and morphometric linkages are empirically defined between wave energy and grain size. Findings indicate that carbonate sediments are primarily sourced from calcifying communities colonizing the outer periphery of the reef platform and that sediment grain size can be reliably linked to wave energy by virtue of a linear model. 相似文献
18.
珊瑚礁支持了对全球气候变化响应最敏感的生态系统之一,其部分特征地貌是海面变化记录的重要载体。目前,无论是对珊瑚礁现代地貌还是埋藏古地貌的研究多以定性为主,定量研究相对匮乏。基于2017年8~9月采集的浅层地震剖面数据,结合遥感影像研究显示,道明群礁目前是发育有1个岛、4个沙洲、7个干出礁和若干座暗礁的典型珊瑚群礁,其形状率为0.11,紧凑度为0.52,延伸率为4.20,礁坪发育指数为0.30,正处于群礁发育早期阶段,为半开放型—准封闭型群礁,远未台礁化,礁体结构遵循Darwin建立的“上截锥型”理论。道明群礁末次冰期以来的古地貌特征揭示了其地貌演化具有阶段性,经历了三个主要的生长期和两次停滞期,表明冰后期海面上升过程中,在相对水深80~90 m和50~60 m处发生停滞;道明群礁现代珊瑚礁开始发育于全新世早期。道明群礁向海坡、礁坪和潟湖盆相关钻孔的采集,将有助于建立可靠的年代标尺与海面变化过程曲线,进一步揭示冰后期南沙北部珊瑚礁地貌发育及其对海面变化的响应。 相似文献
19.
许红 史国宁 廖宝林 陈刚 董树义 邱隆伟 李琦 罗进雄 申剑 曾晓起 王亚民 贺静 董刚 闫桂京 王宇喆 周星蕾 胡喜鹏 罗乔乔 陈竹 陶萌 纳琴 王晴 王英 沈江远 马骁 付和平 吴汉儒 马亚增 陈舒 《古地理学报》2021,23(4):771-788
珊瑚是地球上最古老的原住民,具有近6×108年的发育史,弱势群居、喜温和原地长成是珊瑚的基本特征。作者介绍了珊瑚-珊瑚礁的基本特征,综述了跨十年调查的研究区珍贵照片资料和相关认识,指出中国是全球主要的珊瑚-珊瑚礁国家,地位举足轻重;珊瑚-珊瑚礁作为地球生物多样性的代表,造岛、固礁、护鱼、防护岛岸流失,形成南海四大群岛280余座岛、礁、滩、沙,所构建庞大海洋生态系统是无与伦比的海洋生态资源和寸土寸金的南海海洋国土。提出划分南海珊瑚-珊瑚礁为中央区和周缘区2个分布区,阐述了南海中央区珊瑚-珊瑚礁的基本特征,系统汇集报道了间隔10年2个科考航次调查在浅水礁盘浮潜、至20 m水深浅潜-深潜和礁盘及开展岛、礁、滩、沙地质调查的发现,包括科学定名46种六放石珊瑚和6种八放软珊瑚等成果,同时,收集了西沙、中沙、东沙和南沙群岛海域的相关调查航次珊瑚照片;进一步阐述了单体环礁和复合环礁的特征及分布,并进行了初步对比,指出永乐环礁是南海唯一一个真正的切合达尔文模式的环礁,也是环礁发展到最高阶段的产物,构成现代海洋珊瑚-珊瑚礁形成演化研究最好的天然实验室。 相似文献
20.
Gary M. McMurtry David R. Tappin Peter N. Sedwick Ian Wilkinson Jan Fietzke Bruce Sellwood 《Sedimentary Geology》2007,200(3-4):155-165
Deposits of coral-bearing, marine shell conglomerate exposed at elevations higher than 20 m above present-day mean sea level (MSL) in Bermuda and the Bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage (MIS) 11, ca. 360–420 ka before present. On the strength of this evidence, a sea level highstand more than 20 m higher than present-day MSL was inferred for the MIS 11 interglacial, despite a lack of clear supporting evidence in the oxygen-isotope records of deep-sea sediment cores. We have critically re-examined the elevated marine deposits in Bermuda, and find their geological setting, sedimentary relations, and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period. Rather, these deposits, which comprise a poorly sorted mixture of reef, lagoon and shoreline sediments, appear to have been carried tens of meters inside karst caves, presumably by large waves, at some time earlier than ca. 310–360 ka before present (MIS 9–11). We hypothesize that these deposits are the result of a large tsunami during the mid-Pleistocene, in which Bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll. Likely causes for such a megatsunami are the flank collapse of an Atlantic island volcano, such as the roughly synchronous Julan or Orotava submarine landslides in the Canary Islands, or a giant submarine landslide on the Atlantic continental margin. 相似文献